tailieunhanh - Chapter 048. Acidosis and Alkalosis (Part 5)

Metabolic Acidosis Metabolic acidosis can occur because of an increase in endogenous acid production (such as lactate and ketoacids), loss of bicarbonate (as in diarrhea), or accumulation of endogenous acids (as in renal failure). Metabolic acidosis has profound effects on the respiratory, cardiac, and nervous systems. The fall in blood pH is accompanied by a characteristic increase in ventilation, especially the tidal volume (Kussmaul respiration). Intrinsic cardiac contractility may be depressed, but inotropic function can be normal because of catecholamine release. Both peripheral arterial vasodilation and central venoconstriction can be present; the decrease in central and pulmonary vascular compliance predisposes. | Chapter 048. Acidosis and Alkalosis Part 5 Metabolic Acidosis Metabolic acidosis can occur because of an increase in endogenous acid production such as lactate and ketoacids loss of bicarbonate as in diarrhea or accumulation of endogenous acids as in renal failure . Metabolic acidosis has profound effects on the respiratory cardiac and nervous systems. The fall in blood pH is accompanied by a characteristic increase in ventilation especially the tidal volume Kussmaul respiration . Intrinsic cardiac contractility may be depressed but inotropic function can be normal because of catecholamine release. Both peripheral arterial vasodilation and central venoconstriction can be present the decrease in central and pulmonary vascular compliance predisposes to pulmonary edema with even minimal volume overload. Central nervous system function is depressed with headache lethargy stupor and in some cases even coma. Glucose intolerance may also occur. There are two major categories of clinical metabolic acidosis high-AG and normal-AG or hyperchloremic acidosis Table 48-3 and Table 48-4 . Table 48-4 Causes of High-Anion-Gap Metabolic Acidosis Lactic acidosis Toxins Ketoacidosis Ethylene glycol Diabetic Methanol Alcoholic Salicylates Starvation Propylene glycol Pyroglutamic acid Renal failure acute and chronic Metabolic Acidosis Treatment Treatment of metabolic acidosis with alkali should be reserved for severe acidemia except when the patient has no potential HCO3- in plasma. Potential HCO3- can be estimated from the increment A in the AG AAG patient s AG - 10 . It must be determined if the acid anion in plasma is metabolizable . 0-hydroxybutyrate acetoacetate and lactate or nonmetabolizable anions that accumulate in chronic renal failure and after toxin ingestion . The latter requires return of renal function to replenish the HCO3- deficit a slow and often unpredictable process. Consequently patients with a normal AG acidosis hyperchloremic acidosis a slightly elevated AG .